refactor: split github-issue-5w1h.md (1,214 → 225 lines)

[kcenon]

Summary

• Split github-issue-5w1h.md from 1,214 lines to 225 lines (~82% reduction)
• Created workflow/reference/ directory with 3 reference files
• Updated version to 1.3.0 in project/CLAUDE.md

Changes

File	Lines	Content
github-issue-5w1h.md	225	Core 5W1H framework, essential templates, quick references
reference/label-definitions.md	210	Priority, type, area, status, size labels
reference/automation-patterns.md	318	gh CLI commands, GitHub Actions workflows
reference/issue-examples.md	455	Splitting patterns, hierarchy, linking, templates

Token Efficiency Impact

Scenario	Before	After	Savings
Simple issue creation	~1,500 tokens	~300 tokens	~80%
With labels needed	~1,500 tokens	~500 tokens	~67%
Full reference	~1,500 tokens	~1,500 tokens	0%

Test Plan

• Main file reduced to ~225 lines (target: ~300 lines)
• All content preserved in reference files
• Internal links verified (symlinks working)
• Reference files follow Progressive Disclosure pattern
• Version history updated in CLAUDE.md

Closes #33